1. Field of the Invention
This invention relates to a novel organic silicon compound useful as a surface treating agent for an inorganic filler. It also relates to an inorganic filler surface treated with the organic silicon compound and an electrically insulating composition loaded with the filler.
2. Prior Art
Ethylene-propylene rubber (EPR) and ethylene-propylene-diene terpolymer (EPDM) are widely used as insulators and sheath materials for electric conductors and cables since they have superior heat resistance and weather resistance as well as electrically insulating properties.
However, EPR and EPDM are less resistant to oil and must be loaded with large amounts of inorganic fillers such as clay and talc for improving oil resistance. Rubber compositions loaded with large amounts of inorganic fillers, however, become hygroscopic and suffer from an undesirable drop of electrical insulation.
An attempt was made to improve the moisture resistance of inorganic fillers by treating the fillers with the compound of the following general formula (i). EQU (CH.sub.3 OCH.sub.2 CH.sub.2 O).sub.3 SiCH.dbd.CH.sub.2 (i)
Regrettably, when inorganic materials are surface treated with the compound of formula (i), this compound generates methyl cellosolve which is toxic.
Similar known compounds include vinyltrimethoxysilane, vinyltriethoxysilane and vinylmethyldimethoxysilane. When inorganic materials are treated directly with these compounds, the treatment does not proceed to a full extent on account of their low boiling point, failing to achieve the desired properties.